Faulty Air Fuel Ratio (A/F) Sensor
Air Fuel Ratio Sensor harness is open or shorted
Air Fuel Ratio Sensor circuit poor electrical connection
Faulty Engine Control Module (ECM)
Engine Light ON (or Service Engine Soon Warning Light)
Code P219A Toyota Description
The Air Fuel Ratio (A/F) sensor generates a voltage that corresponds to the actual air-fuel ratio. This sensor voltage is used to provide the Engine Control Module (ECM) with feedback so that it can control the air-fuel ratio. The ECM determines the deviation from the stoichiometric air-fuel ratio level and regulates the fuel injection duration. If the air-fuel ratio sensor malfunctions, the ECM is unable to control the air-fuel ratio accurately.
The air-fuel ratio sensor is a planar type and is integrated with the heater, which heats the solid electrolyte (zirconia element). This heater is controlled by the ECM. When the intake air volume is low (the exhaust gas temperature is low), a current flows into the heater to heat the sensor, in order to facilitate accurate oxygen concentration detection. In addition, the sensor and heater portions are narrow types. The heat generated by the heater is conducted to the solid electrolyte through the alumina, and therefore sensor activation is accelerated.
In order to obtain a high purification rate of the carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOx) components in the exhaust gas, a three-way catalytic converter is used. For the most efficient use of the three-way catalytic converter, the air-fuel ratio must be precisely controlled so that it is always close to the stoichiometric level.
The ECM uses the air-fuel ratio sensor and crankshaft position sensor to monitor the difference in air-fuel ratios between the cylinders caused by differences in injection volumes between the cylinders, leakage in the intake or exhaust system, etc.
When the air-fuel ratios of the cylinders are lean or rich with respect to each other, the ECM determines that there is a malfunction, illuminates the MIL and stores a Diagnostic Trouble Code (DTC).
When the system detects a difference in air-fuel ratios between the cylinders due to fluctuation in the air-fuel ratio sensor output over 1 engine cycle (2 crankshaft revolutions), the ECM determines that there is a malfunction.
P219A Toyota Code – Bank 1 Air-Fuel Ratio Imbalance